Over-heated tonight, strange compression numbers...

[Benshooter]

So I was out and about when my alternator/water pump belt started to shriek and shortly after snapped. I turned around and headed for autozone. As soon thought to look down I had hit 250F. I killed the engine and pulled over. Lots of steam. Anyways I made it to autozone, got a new belt and made it home, stopping to let the car cool down every few miles or whenever it got close to 250.

So I run a compression test and got 105-115 across the board. Wet test saw about a 10psi increase except in number 2, which jumped to 150. After that I reluctantly started the car up. Ran fine, just like before. It has been missing/stuttering slightly between 2000 and 3000 rpm, but nothing that terrible. I didn't check the compression when I got the car a few weeks ago (previous owner said it was a fresh rebuild, silly me) so I don't have a previous test to compare it to.

Based on the results of the wet test, could it be the valve seals? I checked my oil and it's still very clean, no traces of water so I don't think the head is screwed. When the car is idleing or throttled up to 2000/2500rpm, I can hear and feel air leaking out of the valve cover breather(side breather, non pcv) is that air leaking past the valve seals? Should I have the head machined?

Oh and I'm at about 4300' elevation wise. I know it affects compression...

 

[Stockrocks]

If your car ran hot then the question is not "Is there damage" it is "How bad is the damage". Ive had some cars need machining and some just need a new head gasket. When you did the compression test did you write down each cylinders compression and look in a haynes/chilton manual for reference? Did you crank on the engine the exact same intervals on each cylinder? remember just because they all get to 100-115 doesn't matter if you had to crank on one for 10 seconds when the other cylinders just needed 5 seconds.

Im not saying you didn't do the test right i'm just going by how you presented the information, I'd retest and make sure i used the same time intervals cranking on each cylinder and record them and post back, unless of course you did it that way already.

 

[IgotBoost91]

well when a car i had overheated i replaced the headgasket and the compression was still down so i swapped the pistons and it did the trick

 

[95blackGsTurbo]

How many miles are on the car since the motor was probably never freshened. 250* is hot but nowhere near fatal. How did you perform the compression test? All plugs out, MFI fuel pulled with the throttle plate wide open during cranking? VERY unlikely to gain 35-40 psi on a wet compression test.

 

[Benshooter]

How many miles are on the car since the motor was probably never freshened. 250* is hot but nowhere near fatal. How did you perform the compression test? All plugs out, MFI fuel pulled with the throttle plate wide open during cranking? VERY unlikely to gain 35-40 psi on a wet compression test.

the car has 80k but I know it was rebuilt at some point since it has a six bolt bottom end, beehive springs, arp headstuds, cams, oversized pistons, etc. When all this work was done and with what level of quality is unknown. Supposedly it was 5k ago. I should have also mentioned that when I looked down at my water temp and it was at 250F, that's as high as my junk autometer goes. I though I saw a few traces of steam, then I glanced down and "oh sht". So i couldn't accurately say how hot it got.

All plugs out and I had the throttle held wide open with a pair of small vice grips GENTLY holding with a shop rag in the jaws. I unplugged the coil pack but didn't disconnect fuel... Oops.

As far as the results, I don't see a need to be right on the dot with every cylinder as long as it's all within about 10 psi of each other, which is why I took note of the wet test number on 2. But if someone really wants me to test it again I'll do so and record exact numbers.

 

[rhodess89]

there is a kit you can get that have a blue chemical and with the car running and you pump it while its attached to the thermostat housing where you take your cap off if the chemical turns green after a few minutes its sniffing out the hydrocarbons in the coolant system which means there is some kind of gasket leak

 

[One Equals Two]

VERY unlikely to gain 35-40 psi on a wet compression test.

Happens all the time....unless you're referring to DSMs. I've seen jumps as high as 130 psi on a wet test before. (25 to 155 in a Saturn in cylinder 3). And the Civic I tested that came into our shop was similar. 105 then to 150 on a wet test in cylinder 2.

I am guessing that the overheating had nothing to do with your compression numbers. Don't get me wrong, 250 is bad, but if you let it slowly cool down, you should be okay. I think the engine is worn, and possibly has a worn rod bearing. When the angle of the piston is off, a wet test can bring back all kinds of numbers. I've seen 40 psi variations from cranking cycles on the same cylinder within seconds of each other with bearings.

If you have a vacuum gauge, check to see how to test for bad intake valves if you suspect one is bad. However, compression should not be affected by a wet test if a valve is bad. And if a valve is bad, likely you'll have numbers like 0 or 5 psi.

 

[Benshooter]

Happens all the time....unless you're referring to DSMs. I've seen jumps as high as 130 psi on a wet test before. (25 to 155 in a Saturn in cylinder 3). And the Civic I tested that came into our shop was similar. 105 then to 150 on a wet test in cylinder 2.

I am guessing that the overheating had nothing to do with your compression numbers. Don't get me wrong, 250 is bad, but if you let it slowly cool down, you should be okay. I think the engine is worn, and possibly has a worn rod bearing. When the angle of the piston is off, a wet test can bring back all kinds of numbers. I've seen 40 psi variations from cranking cycles on the same cylinder within seconds of each other with bearings.

If you have a vacuum gauge, check to see how to test for bad intake valves if you suspect one is bad. However, compression should not be affected by a wet test if a valve is bad. And if a valve is bad, likely you'll have numbers like 0 or 5 psi.

I'll be doing a couple different things tomorrow to figure this out. I'll have my compressor back so I'll rig up a leak down tester. I'm sure ill be pulling the VC off since the valvetrain is my prime suspect.

My wet test numbers came back between 0-3 psi higher than the dry, so it's not the rings. I did the wet test twice, once with a little oil, then with a capfull. Both yielded nearly identical results.